Basically, it puts a block of color behind links you have visited and changes the color of the text of those links as well. To change the highlight color, change "red" to whatever color you want to be the background of visited links; just make sure to also change the text color of the links so they are still readable by changing "white" to whatever color is easy to read on the background color you choose. Credit goes to numerous other styles on this site for the font color change, the background on the visited links I just happened to stumble across. Comes in really handy on clicksites. Enjoy.

To use this style, install Firefox and Stylish. If you already have Stylish, make sure this site is allowed to run JavaScript.